1. Field of the Invention
The present invention relates to a hard disc drive, and more particularly, to a method of and an apparatus for detecting an actuator vibration in a hard disc drive, and a hard disc drive write control method of avoiding effect due to a read/write head vibration.
2. Description of Related Art
A hard disc drive is a recording apparatus used for storing information. Typically, a hard disc drive includes one or more magnetic recording discs, and information is recorded on concentric tracks in the magnetic recording discs. The discs are loaded on a spindle motor to be rotated, and the information recorded on the magnetic recording discs is accessed by a read/write head installed on an actuator arm rotated by a voice coil motor (VCM). The VCM moves the head by rotating the actuator upon being excited by a current. The read/write head reads the information recorded on a surface of the disc by sensing a change of a magnetic field on the surface of the disc. To write data on tracks, a current is supplied to the head. The current generates a magnetic field, and the magnetic field magnetizes the surface of the disc.
A hard disc drive records/reproduces data in response to a command from a host system.
In the hard disc drive, it is preferable that data be exactly recorded along a center of a track. However, a head typically moves with drifting left and right along a center of a track due to being affected by a response characteristic of a tracking control circuit, inertia of an actuator, and bias conducted to the head. A degree of how far a head is apart from a track center, that is, an off-track, can be detected by a servo burst signal recorded on a servo sector area, and a signal indicating the magnitude of the off-track is commonly called a position error signal (PES).
When the off-track is severe, data recorded on a neighbor track may be erased by a write operation on a target track. Accordingly, in a conventional recording method, a write operation is performed only when a degree of the off-track, i.e., the magnitude of PES, is within a specified limit.
However, in the hard disc drive, it is known that an actuator vibrates according to a magnetic flux density distribution status of the VCM. In particular, since a magnetic flux density distribution of a one magnet VCM is not as even as that of a multi-magnet VCM, the actuator of the one magnet VCM can vibrate easily. This vibration tendency is usually larger in an inner disc zone rather than in an outer disc zone.
The actuator vibration according to the magnetic flux density distribution of the VCM has a unique frequency (however, the frequency is a little bit different according to a hard disc drive) and depends on a seek distance, i.e., a moving distance of the actuator to place a head on a target track, and a seek position, i.e., a position of the target track.
When the actuator vibrates, if the hard disc drive is controlled to record by relying on only the magnitude of PES like in a conventional method, a write operation may be unstable. That is, when the actuator vibrates, since an off-track component due to the vibration and an off-track component due to a drift according to a tracking operation are added, a probability that the PES exceeds a threshold value is higher. This tendency is maintained until the vibration of the actuator exceeds a permitted limit.
On the other hand, it is well known that the magnitude of a write current to the write head is changed according to an operational temperature of the hard disc drive. For example, since a coercive power of a disc increases in an operational environment at a low-temperature, the magnitude of the write current must be larger than in an operational environment at a high or normal temperature. If the actuator vibrates in the operational environment at a low-temperature, a write operation is unstable, and a probability that a neighbor track erase effect is generated is higher.
Therefore, it is preferable that a write operation be performed when the vibration of the actuator is reduced below a permitted limit.